The present invention relates to a device for separating single sheets from a stack of sheets, and more especially to such a device which includes vertically displaceable corner hold-down members in the area of the front corners of the sheets.
German Auslegeschrift No. 2,643,388 discloses a sheet separating device equipped with nearly vertically displaceable corner hold-down members in the area of the front corners of the sheets, each of the hold-down members being attached to one end of a lever which is adapted to be pivoted about a first swivel joint provided at its opposite end, with the two levers being arranged along the two longitudinal sides of the stack of sheets. The lever is also hinged on a second movable swivel joint which forms a part of the lever. On this second swivel joint a control bar having a fixed swivel joint is pivoted. The first swivel joint is displaceably arranged.
This device, in which the corner hold-down members are fastened to pivotable levers, requires a certain expense to obtain a nearly straight-line travel of the corner hold-down members in the area of the front edge of the stack of sheets. For that purpose, a four-membered gear arrangement is necessary and, in addition, the corner hold-down members must be pivoted. In a separating device of this kind, the height of the stack of sheets is limited, because a straight-line motion of the corner hold-down members can only be obtained over a particular vertical range.
In the sheet separating device described in German Offenlegungsschrift No. 2,007,594, the corner hold-down members, which are mounted on swivel arms extending along the outer surfaces of guide bars, execute a substantially vertical movement along a curved path. In order to align the front end of the stack to correspond to this curved path, a front stop device is provided which can be moved into and out of an upright position into contact with the stack. This stop device is equipped with a stop member which is arranged between the corner hold-down members, and the lower end of the stop member is, by appropriate means, firmly connected to a shaft which is rotatably mounted in jaws underneath the tray containing the stack.
This known device is expensive, because, in addition to the arms employed to swivel the corner hold-down members, a separate stop device is provided which must be rotatable about a shaft, in order to take into account the curved downwardly extending path of the corner hold-down members, so that even the lowermost sheets of the stack can be separated without difficulty.
A sheet separating device which is disclosed in German Offenlegungsschrift No. 2,265,108 comprises control means which cause the corner hold-down members to be in substantially constant contact with the corners of the stack, so as to move along a vertically downward path during the separating process. For that purpose, a lever is attached to a side plate which has curved slots for receiving pegs protruding from the lever. When the lever is lifted, the pegs will follow the elongate, curved contour of the slots, whereby the sheet separating member moves substantially vertically downwardly. A cam system is provided for lifting the lever.
This sheet separating device also comprises relatively expensive elements which are necessary to move the corner hold-down members along an approximately vertical path.
In all of the above-described, previously proposed sheet separating devices the height of the stack of sheets is limited, because a straight-line motion of the corner hold-down members can only be achieved over a particular narrow range, and in this regard, additional means must be provided to move the corner hold-down members along a path which extends nearly vertically.